Hello,
this patch binds scanning direction for statements within BB in function
substitute_and_fold with the do_dce flag. For DCE it is profitable to
walk statements
from last to first element, but in non-DCE passes - like VRP - it is
more profitable
to walk opposite direction.
ChangeLog gcc
2011-07-21 Kai Tietz <kti...@redhat.com>
* tree-ssa-propagate.c (substitute_and_fold): Use
do_dce flag to deside, if BB's statements are scanned
in last to first, or first to last order.
Bootstrapped and regression tested for all standard languages
(including Ada and Obj-C++) on
host x86_64-pc-linux-gnu. Ok for apply?
Regards,
Kai
Index: gcc-head/gcc/tree-ssa-propagate.c
===================================================================
--- gcc-head.orig/gcc/tree-ssa-propagate.c
+++ gcc-head/gcc/tree-ssa-propagate.c
@@ -966,6 +966,9 @@ replace_phi_args_in (gimple phi, ssa_pro
DO_DCE is true if trivially dead stmts can be removed.
+ If DO_DCE is true, the statements within a BB are walked from
+ last to first element. Otherwise we scan from first to last element.
+
Return TRUE when something changed. */
bool
@@ -1046,9 +1049,10 @@ substitute_and_fold (ssa_prop_get_value_
for (i = gsi_start_phis (bb); !gsi_end_p (i); gsi_next (&i))
replace_phi_args_in (gsi_stmt (i), get_value_fn);
- /* Propagate known values into stmts. Do a backward walk to expose
- more trivially deletable stmts. */
- for (i = gsi_last_bb (bb); !gsi_end_p (i);)
+ /* Propagate known values into stmts. Do a backward walk if
+ do_dce is true. In some case it exposes
+ more trivially deletable stmts to walk backward. */
+ for (i = (do_dce ? gsi_last_bb (bb) : gsi_start_bb (bb));
!gsi_end_p (i);)
{
bool did_replace;
gimple stmt = gsi_stmt (i);
@@ -1057,7 +1061,10 @@ substitute_and_fold (ssa_prop_get_value_
gimple_stmt_iterator oldi;
oldi = i;
- gsi_prev (&i);
+ if (do_dce)
+ gsi_prev (&i);
+ else
+ gsi_next (&i);
/* Ignore ASSERT_EXPRs. They are used by VRP to generate
range information for names and they are discarded
